1. Field of the Invention
The present invention relates to a charge pump circuit and an amplifier which uses an output of the charge pump circuit as a power supply.
2. Description of the Related Art
Conventionally, a charge pump circuit is used in various circuits. In particular, in various portable devices, because a battery power supply is used, the power supply voltage is limited. On the other hand, in various circuits, there is a demand to use the highest possible power supply voltage to facilitate their operations. For this purpose, a charge pump circuit is often provided to boost a voltage of the battery power supply. A charge pump circuit which uses a capacitor is disclosed in, for example, Japanese Patent Laid-Open Publication No. Hei 7-298607.
However, in the conventional charge pump circuit described above, the voltage at the end of the capacitor changes by a large amount during switching. Therefore, a large current flows to the power supply and to ground at the time of switching and noise appears at the power supply, ground, and output terminal. Although it may be possible to use the conventional charge pump circuit without a problem in a digital circuit, it is difficult to use the conventional charge pump circuit in a semiconductor integrated circuit which handles an analog signal.
For example, when a capacitor (C) of 1 μF is to be charged at 1 V (ΔV) for a time of 1 μsec (Δt), a current of 1 A (ΔI) is necessary. This value can be calculated from an equation, ΔI=(C×ΔV)/Δt. In a semiconductor integrated circuit, however, a current of 1 A is a large current, and when such current flows every time switching takes place, normally noise is generated.